全文获取类型
收费全文 | 2075篇 |
免费 | 11篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 13篇 |
化学工业 | 138篇 |
金属工艺 | 13篇 |
机械仪表 | 20篇 |
建筑科学 | 34篇 |
矿业工程 | 4篇 |
能源动力 | 2篇 |
轻工业 | 121篇 |
水利工程 | 10篇 |
石油天然气 | 4篇 |
无线电 | 67篇 |
一般工业技术 | 74篇 |
冶金工业 | 1510篇 |
原子能技术 | 20篇 |
自动化技术 | 62篇 |
出版年
2019年 | 7篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 36篇 |
2012年 | 11篇 |
2011年 | 20篇 |
2010年 | 18篇 |
2009年 | 14篇 |
2008年 | 16篇 |
2007年 | 23篇 |
2006年 | 20篇 |
2005年 | 13篇 |
2004年 | 19篇 |
2003年 | 22篇 |
2002年 | 16篇 |
2001年 | 24篇 |
2000年 | 21篇 |
1999年 | 54篇 |
1998年 | 436篇 |
1997年 | 254篇 |
1996年 | 185篇 |
1995年 | 95篇 |
1994年 | 85篇 |
1993年 | 90篇 |
1992年 | 26篇 |
1991年 | 28篇 |
1990年 | 35篇 |
1989年 | 37篇 |
1988年 | 42篇 |
1987年 | 29篇 |
1986年 | 34篇 |
1985年 | 30篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 5篇 |
1978年 | 11篇 |
1977年 | 41篇 |
1976年 | 89篇 |
1975年 | 7篇 |
1974年 | 11篇 |
1973年 | 12篇 |
1971年 | 6篇 |
1968年 | 6篇 |
1966年 | 9篇 |
1954年 | 6篇 |
1948年 | 5篇 |
排序方式: 共有2092条查询结果,搜索用时 9 毫秒
1.
2.
3.
4.
PJ Jenkins MA Satta M Simmgen WM Drake C Williamson DG Lowe K Britton SL Chew RV Thakker GM Besser 《Canadian Metallurgical Quarterly》1997,47(6):747-751
We report a patient with a metastatic parathyroid carcinoma and medullary carcinoma of the thyroid. This patient represents a variation of the multiple endocrine neoplasia syndrome (MEN) type 2A. There was no evidence of a phaeochromocytoma. The case illustrates the difficulties that may be encountered in localising the source of PTH secretion; the patient underwent four unsuccessful exploratory operations of the neck and mediastinum before further investigations revealed a single metastatic deposit of parathyroid carcinoma involving the first thoracic vertebra. PCR amplification and sequencing of the RET oncogene from the metastatic parathyroid carcinoma and genomic DNA revealed a heterozygous mutation (Cys634Tyr) in exon 11, as has previously been described to occur in MEN 2A. In addition, loss of tumour heterozygosity was demonstrated at loci from chromosomes 1, 2, 3p, 13q and 16p. This represents the first report of a parathyroid carcinoma in a MEN2A patient, in which the multiple allelic deletions are consistent with the generalised losses observed in aggressive tumours. 相似文献
5.
Cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme in the bile acid biosynthetic pathway, is thought to be regulated by hydrophobic bile acids through negative feedback control. The role of cholesterol in the regulation of cholesterol 7 alpha-hydroxylase is more controversial, in part because of incomplete understanding of the relationship between the pathways of cholesterol synthesis and degradation. The main objective of this study was to define the interaction between these two pathways in an experimental model in which the supply of newly synthesized cholesterol was interrupted by sustained infusion of mevinolin (lovastatin), an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) or accelerated by a continuous infusion of mevalonate, a cholesterol precursor. The study was carried out in rats subjected to short-term bile fistula. In one set of experiments, rats were treated postoperatively with mevinolin (5 mg/kg loading dose followed by 2 mg/kg/hr infusion), mevalonate (180 mumol/hr infusion) or both for up to 96 hr. In a separate set of experiments, rats were infused intraduodenally with taurocholate (36 mumol/100 gm/hr for up to 96 hr). We determined cholesterol 7 alpha-hydroxylase- and HMG-CoA reductase specific activities at those time intervals, whereas bile acid synthesis rates were determined throughout the study. Compared with rats not subjected to surgery, rats with short-term biliary diversion had increases in cholesterol 7 alpha-hydroxylase activity of 259% and 827% at 48 and 96 hr, respectively. The increase in bile acid biosynthesis was less pronounced. Continuous infusion of mevinolin completely prevented increases in cholesterol 7 alpha-hydroxylase specific activity and bile acid biosynthesis at both time intervals.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
6.
7.
AR Santos JC Nery NC Duppre ME Gallo JT Filho PN Suffys WM Degrave 《Canadian Metallurgical Quarterly》1997,46(2):170-172
A case is described in which a pericardial branch of a nongrafted left internal mammary artery communicated directly with the distal left anterior descending artery, following saphenous vein bypass grafting. This type of collateralization following coronary artery bypass surgery seems to be very rare, and perhaps could protect the myocardium from severe ischemia. 相似文献
8.
Microllular plastics are cellular polymers characterized by cell densities greater than 109 cells/cm3 and cells smaller than 10 μm. One of the critical steps in the continuous production of microcellular plastics is the promotion of high cell nucleation rates in a flowing polymer matrix. These high nucleation rates can be achieved by first forming a polymer/gas solution followed by rapidly decreasing the solubility of gas in the polymer. Since, in the processing range of interest, the gas solubility in the polymer decreases as the pressure decreases, a rapid pressure drop element, consisting of a nozzle, has been employed as a continuous microcellular nucleation device. In this paper, the effects of the pressure drop rate on the nucleation of cells and the cell density are discussed. The experimental results indicate that both the magnitude and the cell density are discussed. The experimental results indicate that both the magnitude and the rate of pressure drop play a strong role in microcellular processing. The pressure phenomenon affects the thermodynamic instability induced in the polymer/gas solution and the competition between cell nucleation and growth. 相似文献
9.
Dandeneau Stéphane D.; Baldwin Mark W.; Baccus Jodene R.; Sakellaropoulo Maya; Pruessner Jens C. 《Canadian Metallurgical Quarterly》2007,93(4):651
Personality processes relating to social perception have been shown to play a significant role in the experience of stress. In 5 studies, the authors demonstrate that early stage attentional processes influence the perception of social threat and modify the human stress response. The authors first show that cortisol release in response to a stressful situation correlates with selective attention toward social threat. Second, the authors show in 2 laboratory studies that this attentional pattern, most evident among individuals with low self-esteem, can be modified with a repetitive training task. Next, in a field study, students trained to modify their attentional pattern to reduce vigilance for social threat showed lower self-reported stress related to their final exam. In a final field study with telemarketers, the attentional training task led to increased self-esteem, decreased cortisol and perceived stress responses, higher confidence, and greater work performance. Taken together, these results demonstrate the impact of antecedent-focused strategies on the late-stage consequences of social stress. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.